OFFSET
1,2
FORMULA
Series_Reversion(A(x)) = F(F(x)) = F(x) + x^2 where F(x) = g.f. of A138740.
EXAMPLE
A(x) = x - 2*x^2 + 10*x^3 - 69*x^4 + 568*x^5 - 5250*x^6 + 52792*x^7 -+...
Let G(x) = x - A(x)^2 = g.f. of A139702:
G(x) = x - x^2 + 4*x^3 - 24*x^4 + 178*x^5 - 1512*x^6 + 14152*x^7 -+...
then A(x) = G(G(x)).
PROG
(PARI) {a(n)=local(A=x); if(n<1, 0, for(i=1, n, A=serreverse(x + (A+x*O(x^n))^2)); polcoeff(subst(A, x, A+x*O(x^n)), n))}
CROSSREFS
KEYWORD
sign
AUTHOR
Paul D. Hanna, Apr 30 2008
STATUS
approved